WO2014044300A1

WO2014044300A1 - Method and device for allocating transmission resources

Info

Publication number: WO2014044300A1
Application number: PCT/EP2012/068411
Authority: WO
Inventors: Kari SEPPÄNEN; Jorma KILPI; Tapio Suihko
Original assignee: Nokia Siemens Networks Oy
Priority date: 2012-09-19
Filing date: 2012-09-19
Publication date: 2014-03-27

Abstract

A method and a device are provided for allocating, in cycles, resources of a transmission medium to data streams for multiplexed transmission of said data streams via said transmission medium. According to the invention, for each cycle, a share of the resources to each of the data streams is allocated and for each cycle the allocation is assessed depending on the allocation of a previous cycle. Furthermore, for each cycle, a size of each share depending on a traffic demand of at least one of the data streams may be determined and the allocation may be performed such that for each cycle the sequence of the data streams in the allocation is altered.

Description

Description Method and device for allocating transmission resources

The invention relates to a method and a device for allocating transmission resources, for example in time division

multiplexing environments, and to a communication system.

In current communication networks information may be

transmitted in multiple ways over different transmission paths, e.g. depending on the characteristics and the

architecture of the transmission network. In certain cases multiple senders or information streams may share the same transmission path or channel for their respective

communications. In such cases, well-known methods for organizing the path allocation or the path sharing may be applied .

One of the most common methods to make one single

transmission path available for multiple senders is the so- called "multiplexing" process. In telecommunications and computer networks, multiplexing (also known as muxing) is a method wherein multiple analog signals or digital data streams are combined into one signal over the transmission path or, more generally, a shared medium. For example, in telecommunications, several telephone calls may be carried simultaneously via one wire.

The multiplexed signal is transmitted over the transmission path, which may comprise at least one of a physical

transmission medium, logical transmission link or a

communication channel e.g. within a physical transmission medium or a logical link. In the following the term

communication link is used to denote a shared medium

providing transmission resources for communications.

Information to be communicated may be modulated and/or coded onto/into analog or digital data streams. By multiplexing the capacity of the communication channel is subdivided into several sub-channels, one for each analog signal or digital data stream to be transferred. On the receiver side the original signals can be extracted by means of a reverse process, known as demultiplexing.

A device that performs multiplexing is called a multiplexer, and a device that performs the reverse process is called a demultiplexer .

Several types of multiplexing technologies are known and in use, for example code division multiplexing (CDM), freguency- division multiplexing (FDM) and time-division multiplexing (TDM) .

Code division multiplexing (CDM) is a class of technigues where several communications share the same freguency spectrum simultaneously. All communications, each with a different code, can be transmitted on the same medium, e.g. a wire, a fiber, a radio channel or other medium. Code Division Multiplexing is used, for example, for mobile phone service and in wireless networks.

Freguency division multiplexing (FDM) is a technigue by which the total bandwidth available in a communication medium is divided into a series of non-overlapping freguency sub-bands, each of which is used to carry a separate signal or data stream. A variant technology, called wavelength-division multiplexing (WDM) is used in optical communications, for example .

Time division multiplexing (TDM) is a type of mostly digital multiplexing in which two or more bit (or data) streams or signals are transferred apparently simultaneously as subchannels in one communication channel, but are physically taking turns on the channel. The time domain is divided into recurrent cycles (or frames), each cycle is subdivided into several time slots, one for each sub-channel. After multiplexing, data of sub-channel 1 (originating from a sender 1, for example) is transmitted during time slot 1, data of sub-channel 2 (from sender 2) is transmitted during time slot 2, and so on. Periodic repetition of the cycles enables continuous communications .

A technigue related to TDM is time-division duplexing (TDD) . A duplex communication system is a point-to-point system composed of two connected parties or devices that can communicate with one another in both directions

simultaneously. If the same link or transmission path for data is used in both directions time-division duplexing (TDD) may be used. TDD is the application of time-division

multiplexing to separate outward and return signals, i.e. time slots are assigned to the senders on both ends of the transmission link, so that within a time slot the

transmission is always performed in only one single

direction .

Synchronous multiplexing systems are characterized by a recurrent cycle or frame structure as mentioned above . So called frame headers and/or trailers are e.g. used for synchronization and error correction between multiplexers and demultiplexers and can also be used for managing resource allocation in consecutive cycles, when e.g. signals or data streams enter or leave the multiplexed community.

On the contrary asynchronous multiplexing systems have no frame structure and organize the transmission either based on fixed length or variable length cells or packets (see e.g. Asynchronous Transfer Mode (ATM) , Ethernet or IP based systems ) .

Whereas asynchronous multiplexing systems are known to inherently offer flexible resource allocation to varying bandwidth and data transmission demands of communications, synchronous systems usually provide static transmission resources for each sub-channel. Early systems based on FDM and TDM, and primarily used for telephony, offered fixed and equal bandwidth for all tributaries. Typical representatives from TDM side are telephone systems using Tl or El based transmission capable of carrying 24 or 30 simultaneous phone calls in equally sized sub-channels, i.e. with identically repeated and equally subdivided frames structures.

Synchronous transmission system like SDH and SONET are capable of providing sub-channels with different transmission rates, often also called tributaries or containers, but cannot accomodate to dynamically changing demands within the tributaries. This often results in a rather inefficient use and/or waste of resources.

Thus, generally with multiplexing and, more specifically, with TDM and TDD disadvantages may arise when different sources sharing one transmission path have a different amount of data to be transmitted. If, for example, time slots are allocated to data sources where at least one of the sources has little or no information at all to be transmitted bandwidth on the transmission path may be wasted.

Generally, when one or more time slots cannot be filled (completely) in a TDM transmission system bandwidth is wasted which, in turn, means additional costs to be spent by the network provider. This similarly applied to CDM, FDM or systems based on other technologies, whenever a contributing source has no or less information to be transmitted than the capacity of the transmission system provided for that source in a given cycle .

An object of the present invention is to overcome the deficiencies mentioned above and, more particularly, to improve multiplex or duplex transmission methods and systems by improving the resource allocation process. The object is achieved with method, a device and a system according to the features of the independent claims . Further embodiments are described in the depending claims .

According to the invention a method is provided for

allocating, in cycles, resources of a transmission medium to data streams for multiplexed transmission of said data streams via said transmission medium, comprising the steps of allocating, for each cycle, a share of the resources to each of the data streams and assessing the allocation depending on the allocation of a previous cycle.

The method may also comprise the step of determining, for each cycle, a size of each share depending on a traffic demand of at least one of the data streams. Thus, the allocation can be based on the current needs for each of the data streams .

In one embodiment a seguence of the data streams in the allocation of a share of the resources to the data streams may be altered for each cycle. Advantageously, each data stream may be in different positions in the seguence of allocation, resulting in different resource shares.

One aspect of the invention is that the allocation may be assessed for each cycle also in consideration of the shares and the allocation seguence of a previous cycle.

In another embodiment of the invention a data stream being first in the allocation of share of resources to data streams has the right for allocation of at least a minimal share. The minimal share may be at least egual to a default share allocated to said data stream, for example.

In yet another embodiment of the invention the share

allocated to a data stream being first in the allocation of share of resources to data streams is allocated according to its current demand, but not greater than the maximum of either its share allocated in the previous cycle or its default share .

Furthermore, the share allocated to a data stream being last in the allocation of share of resources to data streams could be allocated according to its current demand, for example. It may cover the complete resources not yet allocated to other data streams for that cycle. In one embodiment the share allocated to a data stream being neither first nor last in the allocation of share of

resources to data streams is allocated according to its current demand. Preferably, it should not be greater than its share allocated in the previous cycle.

In another embodiment the share of resources allocated to a data stream within a cycle may not be greater than its share in the preceding cycle unless that data stream is first or last in the allocation of share of resources within that cycle.

In one exemplary embodiment the resources could be a

transmission capacity. Furthermore, the resources may be shared, for example, with respect to time and/or freguency.

According to the invention also a device for allocating, in cycles, resources of a transmission medium to data streams for transmission of said data streams via said transmission medium is provided. The device may comprise an allocating unit configured to, for a cycle, allocate a share of the resources to each of the data streams, and an assessing unit configured to assess the allocation depending on the

allocation of a previous cycle. In an embodiment the device further comprises a size

determining unit configured to, for each cycle, determine a size of each share depending on a traffic demand of at least one of the data streams. The assessing unit may be designed such that for each cycle a sequence of the data streams in the allocation of a share of the resources to the data streams is altered.

In one example of the present invention a transmitting device for transmitting data streams via a transmission medium may comprising or be a device as claimed. Also, a communication system comprising a suchlike device may be an implementation example of the present invention.

Certain embodiments of the invention are now explained in greater detail with the help of the following figures, wherein :

Fig. 1 shows usage of resources in a two slot system with fixed, equal size slots, when one of the sources does not fully use its allocated resources,

Fig. 2 shows an allocation of resources for use by data streams in a two slot system according to the invention,

Fig. 3 shows an embodiment of a communication system

according to the present invention, and

Fig. 4 shows a flowchart illustrating the inventive method.

In the embodiments described below transmission resources of a transmission medium are shared between multiple senders. I.e. multiple data streams are multiplexed on one shared transmission medium. Unless otherwise specified, in the examples below, the transmission medium (transmission channel or path) is shared in the time domain. This means that for each sender (or each data stream, respectively) a certain time slot is used within each cycle. Each data stream is allocated to a time slot. However, the invention is not limited to TDM or TDD. Fig. 1 shows the usage of resources in a two slot system with fixed, egual size slots . In case the capacity of the system is subdivided in time, i.e. the full system capacity is dedicated to one single source only at each specific instance of time, it shows the allocation or assignment of time slots in a TDM system according to current TDM technigues. In the system of Fig. 1 two data streams (stream A from a sender A and stream B from a sender B) share the resources of one communication channel. In this example, for each data stream a time slot is defined (time slot 1 for data stream A; time slot 2 for data stream B) . Both time slots 1 and 2 have a fixed length 1/2. In Fig. 1 four consecutive time slot cycles are shown, each time slot cycle having the length 1. Assume that sender A has enough data to fill all available time slots 1, whereas sender B only has limited data to send. As can be seen from Fig. 1 all time slots 1 are used, but the time slots 2 assigned to sender B are only partly filled (see cycle 3) . Thus, bandwidth actually available but assigned to sender B is not used and wasted.

In contrast to this Fig. 2 shows four time slot cycles according to the present inventive method. Again, two different data streams (A and B) are allocated to two time slots per cycle. Note, however, that the invention is not limited to only two different senders and/or two shares of the available transmission resource per cycle (i.e., in this example, two slots per cycle) . It is also in the scope of the present invention to provide a method, respective devices and a system using a plurality of different data streams (or senders) and a plurality of shares (or slots) per cycle. The number of shares could be based on or be egual to the number of data streams. Also, a change in the number of streams and/or shares per cycle could occur, for example

automatically depending on current needs with respect to the transmission link. Typical situations would be a sender or source ending its communications or a new source indicating a communication demand. Furthermore, as already mentioned above also the transmission direction of the data streams to be transmitted is not limited. The transmission may be performed in one direction only or bidirectional whereby, in case of more than two data streams, each data stream may run in either direction.

In the embodiment depicted in Fig. 2 seguence (of the allocation of the data streams and, in this example, the actual transmission of the streams) and length of time slots 1 and 2 are varied. Particularly, two variations are

performed in this example. First, the time slot assignment (i.e. the data stream allocation) is altered. This means that, in this example, in the first cycle data stream A is first to be allocated a share of the transmission resource (here this means it is assigned to time slot 1) and data stream B is second in the allocation process (here: it is assigned to time slot 2) . In the second cycle the assignment is switched, meaning that now data stream A is transmitted during time slot 2 and data stream B during time slot 1 (in fact, the allocation seguence is switched) . Furthermore, again referring to the second cycle, the length of the respective time slots is adapted according to the following rule: the (maximal) length for data stream 2 (now using time slot 1) is defined as the maximum of the length of previous time slot 2 and half of the length of a time slot cycle. The available length for data stream A (using time slot 2) is, then, defined as the remaining time of each time slot cycle. Note, however, that this rule is only mentioned as an example. Any rules stated herein may be amended in any way according to current circumstances or to reguests and desire of the network operator .

The example depicted in Fig. 2 is now described in even greater detail. In the example shown in Fig. 2 it is assumed, again, that sender A has enough data to fill all available time slots. Sender B, as above, only has a limited amount of data to be transmitted. Furthermore, in this example, both senders A and B always get a default share or "fair share" (see below) of 50% of the available resources.

In this embodiment, the capacity of the transmission link is shared in time domain using time slot cycles having a fixed length 1 (this means, in other words, that the sum of the lengths of time slot 1 and time slot 2 or the length of one time slot cycle is constant) . Furthermore, referring to Fig. 2, for each time slot cycle, the first time slot is referred to as time slot 1, the second time slot is called time slot

2. As already mentioned above, the sequence of the allocation of share of transmission resource to sender is altered, which is, for this example, equivalent to altering the assignment of sender to time slot. I.e. if sender A is sending in time slot 1 and sender B is sending in time slot 2 in a first time slot cycle, then, in the subsequent cycle, sender B will send during time slot 1 and sender A will use time slot 2 for sending . Note that, as mentioned above, generally it is the sequence in which (transmission) resources are allocated to the plurality of users (i.e. data streams) that is altered.

Primarily to increase clarity, in the embodiment depicted in Fig. 2 the sequence of allocation of the share of

transmission resource is corresponding to the sequence in which the specific users (data streams) are subsequently transmitted. The invention, however, is in no ways limited to this example. Referring again to Fig. 2, the capacity of the time slot cycles is shared in the following way. For each sender at least the length of the previous time slot 2 (i.e. when the respective sender was assigned to time slot 2) is stored. When a sender turns to be the sender now using time slot 1, said sender can use (for its time slot 1) a - maximal - length which is equal to the maximum of the length of the previous time slot 2 and the half of the length of a time slot cycle (i.e. at least 50% of a time slot cycle). The remaining part of the time slot cycle is then, as time slot 2, assigned to the other sender.

Again, the example of "half of the length of a time slot cycle" is only to be considered an embodiment. In this case both data streams could use under normal operation in full mode 50% of the transmission resource, i.e. each data stream could use a time slot with the length of half the length of a full time slot cycle. This share of 50% can be regarded as the default share (fair share) .

Note that the turnaround (the switch from time slot 1 to time slot 2) is either done when time slot 1 is over or, also, directly when all data is sent - i.e. the actual length of time slot 1 may be shorter than the maximum allowed if there is not enough data to fill the entire time slot.

With respect again to Fig. 2 this means that in time slot cycle 1, time slot 1 is filled with data of sender A, time slot 2 is filled with data of sender B. In the next cycle sender B uses time slot 1. The maximal available time (length of time slot 1) is defined as the length of previous time slot 2 (which is, in this case, also egual to the half of a time slot cycle) . As, in this example, sender B does not have enough data to fill up the whole time slot theoretically available, the turnaround to time slot 2 is done immediately when all data is sent by sender B. The remaining time of the cycle (time slot 2) is then completely used by sender A in this cycle. In the next cycle, cycle 3, time slot 1 is again assigned to sender A. In this cycle the length of time slot 1 (available time for sender A) is egual now to the length of previous time slot 2. I.e. that sender A has more than half of the length of the time slot cycle available. The remaining part of the time slot cycle is, again, assigned to sender B. If, as is the case in this example, sender B meanwhile gets new data to restart sending, time slot 2 is used for this data. In the next cycle sender B (that is now using time slot 1) can use not only the length of the previous time slot, but - as always - at least the length of half of the time slot cycle (if needed) .

This means that the lengths of the different time slots are adjusted dynamically to the needs of the different senders / transmitters. With the present method of using an alternation in the seguence of the allocation, i.e. by using alternating sending slots, it is possible that a sender that does not need its share of resources or transport capacity at one moment can temporarily allocate the spare transmission capacity to the other sender and automatically regain the capacity when it needs more capacity.

According to the present invention and the example of Fig. 2 this means that when one transmitter (e.g. sender B) has very little or no data to send when it is first in the allocation process (when it is assigned to time slot 1), this time slot 1 will be shorter than half of the length of a time slot cycle. As the switch to time slot 2 is performed immediately when all data is sent for time slot 1 sender A may use the remaining time of the time slot cycle (time slot 2) . In the next time slot cycle sender A may still use more than half of the time slot cycle capacity as user of time slot 1 as it is allowed to use a time slot length of up to the same length as it used when it was sender during time slot 2 in the previous time slot cycle. When sender B gets more data to send it can reclaim its share of the time slot cycle capacity the next time it becomes sender using a time slot 1 as it can always use at least one half of the time slot cycle. Thus, a transmitter using the first slot can always gain its fair share, i.e. a minimal share of the transmission resources.

As mentioned before, the example described above is only to be seen as one possible embodiment of the invention. It should be noted that it will be obvious for anyone skilled in the art that many variations and modifications can be made to the preferred embodiment - specifically, but not limited to the rules for the length of the time slots - without substantially departing from the general principles of the present invention. All such variations and modifications are intended to be included herein within the scope of the present invention. For example, further features of the present invention may be as follows.

The default capacity sharing may, for example, also be asymmetric so that one sender is preferred and gets more capacity when both senders operate in full load, i.e. in situations where a complete time slot cycle is used and both senders still have enough data to send during the subseguent time slot cycle. In this case predetermined values for the default time slot length for each of the senders may be used. That means that instead of using half of the length of a time slot cycle for both senders, sender A may, for example, obtain 70% of the time slot cycle (0.7 * "time slot cycle length") and sender B may obtain 30% of the cycle.

Conseguently, this would result in sharing the capacity available in a 70/30 ratio under full load operation.

Generally, the default (or fair) share of a data stream is the amount of resources made available on average for that data stream, if the system runs under continuous full load conditions. The default share of a data stream is a value between 0 and 1 (or 0 and 100%) and, normally, it is assigned to the data stream before it is accepted for transmission. The default share is used under certain conditions for determining the share of resources allocated to that data stream within a cycle of transmission. The sum of the default shares of all accepted data streams is usually not greater than 1 (100%) . However, under the assumption of a statistical behavior of the data streams a so called "overbooking", i.e. an assignment of default shares summing up to more than 100% of the cycle capacity is possible, with the risk of a potential loss of data in case of massive congestion.

A further embodiment of the invention could use an additional time slot for idle situations. If both senders are in an idle state (i.e. no data is to be transmitted) unnecessary delay may occur when data arrives during a time slot cycle. For such situations a further time slot could be added (time slot 3, when referring to the above example) . If the sender currently using time slot 2 has no data to send, time slot 2 may be divided into two parts (namely, time slot 2 and time slot 3) and time slot 3 may be assigned to the other sender, i.e. a new turnaround is performed. With this, the time the other sender has to wait until its time slot appears can advantageously be decreased. Time slots 2 and 3 could have egual lengths, for example, but the respective lengths can also be set to any other value as desired.

In another embodiment time slot 2 may always obtain a minimal slot length, so that some minimum capacity for the sender using time slot 2 is guaranteed. (Or, in other words, the sender using time slot 2 always gets some minimal time for sending.) This could be achieved by, for example, setting a maximal length for time slot 1, meaning that, if desired, time slot 1 can never consume the whole (or most of the) time slot cycle, even if the above rule would result in a

respectively long time slot 1. For example, the amended rule could read as : the time available for the sender using time slot 1, i.e. the length of time slot 1, is defined as the minimum of the maximal length for time slot 1 and the maximum of the length of the previous time slot 2 and half of the length of a time slot cycle. In this case by setting a maximal length for time slot 1 a certain minimal capacity is reserved for time slot 2.

Moreover, the present invention is also applicable with multiplex systems when more than two senders are present. By altering the time slots assigned to the multiple senders the time slot lengths can automatically be adapted to the different data or traffic load situations for the different senders. One embodiment would be to keep the above rule for time slot 1 (meaning that the length of time slot 1 is depending on the length of the previous time slot assigned to the sender now using time slot 1) and to allocate the remaining time of the time slot cycle to the remaining senders (each sender obtaining an individual time slot) . This allocation, in turn, may also be performed according to predetermined rules - the remaining time may be divided egually or again based on the lengths of the respective time slots in previous time slot cycles.

In a system with more than two different data streams the varying of the assignment of data streams to slots may be performed in a cyclic or random way or according to a predetermined rule. For example, for four data streams (A, B, C, D) the succession or seguence of the slot allocation could be changed through subseguent cycles in a forward direction (ABCD - BCDA - CDAB - DABC) or backwards (ABCD - DABC - CDAB - BCDA) . The change could also follow a certain instruction, for example, in a subseguent cycle slot 1 is allocated to the user of previous slot 3, slot 2 is allocated to user of previous slot 1, slot 3 to the user of previous slot 4 and slot 4 to the user of previous slot 2 (ABCD - CADB - DCBA - BDAC) .

It may also be advantageous to allocate "priority rights" to one or more of the data streams. With a preferred processing the respective data stream could, for example, be allocated to slot 1 of the next cycle (or every second cycle or the like), meaning that said stream obtains the right to claim a minimal slot length corresponding at least to its default share for transmission of its data. These priority rights may be assigned to the different senders according to any one or a combination of different criteria such as e.g. a traffic class, specific QoS reguirements , or current traffic demand, that may have been announced or can be measured e.g. by a data buffer occupation. Decision criteria may be modified between the cycles if desired.

By ensuring that the sender being first during share

allocation (in the example above, the sender assigned to the first slot (slot 1) of a cycle) always gains the right to obtain a certain minimum amount of resources (default or fair share), the respective sender always has the possibility to regain transmission capacity lost during cycles with later allocation positions, if necessary.

It should be noted again, that it is not reguired to

physically change the seguence of transmission of the data streams within the time slots of the different cycles as long as the seguence in the allocation of the slot resources for the different streams follows the respective change rules. When respective resources for a cycle have been assigned it does not matter whether a data stream transmits its share as first, second, or in a later position within the cycle.

Furthermore, and amongst other things, the present invention has the further advantage that there is no need to transfer any kind of explicit control information (like reguests, grants, etc.) between the end points of the shared medium (especially, when working in duplex mode) as the present invention can solely rely on implicit information deducted from the transmission path or link usage. Also, there is no need to estimate traffic flow intensities, available capacity or the like. The present invention is, moreover, adapting very fast on changed circumstances enabling each system to react in just a couple of cycles to adjust to changes in the data or traffic load situation.

Fig. 3 shows an implementation embodiment of the example depicted in Fig. 2. In Fig. 3 a first transceiver Tl and a second transceiver T2 are located in a communication system or network N. Tl and T2 are connected via a transmission link M. The link M (or transmission path) may be designed as a shared medium. For sending and receiving data or data streams (indicated by arrows in Fig. 3) between Tl and T2 the present invention can be utilized. The shared medium may be used according to a time duplex method, i.e. that data is sent from Tl and received by T2 in a first time slot and data is transmitted in the other direction (sent by T2 and received by Tl) during a second time slot. Before the actual

transmission of the data the data streams are prepared according to the present invention. This preparation

comprises allocating resources to the data streams, i.e.

assigning the data streams to specific time slots. (This process is also known as "framing" as the slot cycles are also referred to as frames) . Thus, the transceivers may contain a transmitter S, a receiver R and a framer F.

Operation of the framer may be controlled either locally on each side or by means of a centralized control or management device (not shown) . Furthermore, it is also possible that the framing or scheduling is completely performed by a central management unit, sometimes referred to as a "scheduler".

Note, however, that according to the invention transceivers Tl and T2 of Fig. 3 may also represent sender and receiver in a multiplex environment .

One application area for the present invention may be fault- tolerant, high-capacity wireless mesh networks for cellular backhaul .

It is to be noted that the invention is not limited to time division multiplexing and/or duplexing. Also, a splitting with respect to, for example, freguencies or any other well- known domain is within the scope of the invention. As to freguency multiplexing or duplexing a slot may be a certain freguency band or freguency subchannel that can be assigned to a certain sender. In this case the allocation of freguency to data streams could be altered, i.e. for each cycle a different data stream is picked first for allocation.

Furthermore, when one sender has no data left for

transmission the respective sender may give away a part of its share of the available freguency band. In the next cycle this last freguency split may serve as basis for the next allocation according to the rules determined beforehand. Finally, a more general approach to the inventive method is now presented with help of the flow chart of Fig. 4. Fig. 4 shows method steps for one cycle and, more particularly, steps for assessing the allocation of resources. After start of a cycle x (400) in a first step the seguence of the data streams in the assignment of resources and the actual resource assignment of the previous cycle x-1 are retrieved (step 401) . In the next step, step 402, the current traffic demands of the data stream for the current cycle x are checked. From this the seguence of the data streams in the allocation process for the current cycle x is determined (step 403) . In step 404 the resources for the first data stream in the allocation process are assigned to the first data stream.

A general rule could be to assign the resources for the first data stream in the following way: the resource maximum for the first data stream is defined as the maximum of the assigned resources for the respective data stream in the previous cycle x-1 and the default share defined for this data stream. If this resource maximum is greater than the current traffic demand of this data stream in the current cycle x, then the assigned resources are set as the resources needed for the traffic demand only. If the resource maximum is smaller than the resources needed to cover the demand, then the assigned resources are set to the maximum allowed.

In step 405 the next data stream in the seguence of data streams is chosen. In step 406 it is determined, for the chosen data stream, whether this data stream is the last data stream in the seguence of data streams . If this is not the case then, in step 407, resources are assigned to this data stream according to a specific rule and the method jumps back to step 405 to choose the next data stream in the seguence. The rule for the data stream being neither first nor last in the seguence of data streams may be defined in the following way: the resources assigned to the respective data stream in the current cycle x are defined as generally being egual to the resources assigned to this data stream in the previous cycle x-1. Only if the traffic demand is smaller than these resources then the assigned resources are, conseguently, only as great as reguired for the current traffic demand.

If in step 406 it is determined that the next data stream in the seguence of allocation is the last data stream to get resources assigned to then the method continues with step 408 and resources are assigned to this data stream. This may be handled according to the following rule: generally, the resource assigned to the last data stream is egual to the remaining resources of the current cycle x. If, however, the traffic demand of this last data stream is smaller than the rest of the resources of this cycle x, then only the reguired resources are allocated to the last data stream. After allocation of resources to the last data stream within cycle x, cycle x ends at step 409.

As shown above, different rules for the allocation of resources to the data streams may be applied for the first, the last as well as the remaining data streams in the allocation process. Furthermore, note that step 402 may only be optional at this point. Checking the current traffic demand before determining the seguence is only necessary in case of prioritized seguencing. If the seguence in the allocation is altered independent of current traffic demands (e.g. in case of a cyclic change in the allocation seguence) step 402 may also be omitted. (However, the traffic demand may always be checked when actually assigning resources according to the rules described above.)

Also, if after assigning resources to the last data stream in step 408 resources are left in the current cycle (i.e. if the traffic demand of the last data stream is smaller than the remaining resources) the remaining resources of the current cycle may be assigned to any of the further data streams. This, again, may depend on predetermined rules, i.e. on priority and/or traffic demand, for example. The method as laid out in the flow chart of Fig. 4 may suspend when the remaining resources in cycle x are not sufficient to fully allocate the resources assigned to a data stream being on turn to get resources allocated. It may happen that a data stream receives less resources than the rules indicate or even no resources at all for a certain cycle. A suchlike situation is more likely in case of overbooking of resources than with a more conservative admission strategy.

Claims

Claims :

1. A method for allocating, in cycles, resources of a transmission medium to data streams for multiplexed

transmission of said data streams via said transmission medium, comprising the steps of:

- for each cycle, allocating a share of the resources to each of the data streams, and

- assessing the allocation depending on the allocation of a previous cycle.

2. The method according to claim 1, comprising the step of, for each cycle, determining a size of each share depending on a traffic demand of at least one of the data streams.

3. The method according to claim 1 or 2, wherein for each cycle a seguence of the data streams in the allocation of a share of the resources to the data streams is altered.

4. The method according to any of the preceding claims, wherein a data stream being first in the allocation of share of resources to data streams has the right for allocation of at least a minimal share.

5. The method according to claim 4, wherein the minimal share is at least egual to a default share allocated to said data stream.

6. The method according to any of the preceding claims, wherein the share allocated to a data stream being first in the allocation of share of resources to data streams is allocated according to its current demand, but not greater than the maximum of either its share allocated in the previous cycle or its default share.

7. The method according to any of the preceding claims, wherein the share allocated to a data stream being last in the allocation of share of resources to data streams is allocated according to its current demand, but may cover the complete resources not yet allocated to other data streams for that cycle.

8. The method according to any of the preceding claims, wherein the share allocated to a data stream being neither first nor last in the allocation of share of resources to data streams is allocated according to its current demand, but not greater than its share allocated in the previous cycle.

9. The method according to any of the preceding claims, wherein the share of resources allocated to a data stream within a cycle is not greater than its share in the preceding cycle unless that data stream is first or last in the allocation of share of resources within that cycle.

10. The method according to any of the preceding claims, wherein the resources are a transmission capacity.

11. The method according to any of the preceding claims, wherein the resources are shared with respect to at least one of :

- time

- freguency.

12. A device for allocating, in cycles, resources of a transmission medium to data streams for transmission of said data streams via said transmission medium, comprising:

- an allocating unit configured to, for a cycle, allocate a share of the resources to each of the data streams, and - an assessing unit configured to assess the allocation depending on the allocation of a previous cycle.

13. The device according to claim 10, further comprising a size determining unit configured to, for each cycle,

determine a size of each share depending on a traffic demand of at least one of the data streams .

14. The device according to claims 12 or 13, wherein the assessing unit is designed such that for each cycle a seguence of the data streams in the allocation of a share of the resources to the data streams is altered.

15. The device according to any of claims 12 to 14, wherein the allocating unit is designed such that a data stream being first in the allocation of share of resources to data streams has the right for allocation of at least a minimal share.

16. The device according to claim 15, wherein the allocating unit is designed such that the minimal share is at least egual to a default share allocated to said data stream.

17. A transmitting device for transmitting data streams via a transmission medium comprising a device according to any of claims 12 to 16.

18. A communication system comprising a device according to any of claims 12 to 16.